Description of problem: Currently vms in userspace (qemu:///session) can not communicate with each other. To enable this it would be nice if there was an option to set a mcast domain for the user networking, that way vms could communicate via that domain and would be connected. I.e.: <qemu:arg value='-netdev'/> <qemu:arg value='socket,id=busnet0,mcast=230.0.0.1:1234'/> <qemu:arg value='-device'/> <qemu:arg value='virtio-net-pci,netdev=busnet0,id=net1,mac=52:54:00:4b:9b:11'/>
Unless I'm missing some detail, this was recently implemented (in libvirt 1.2.20): https://libvirt.org/formatdomain.html#elementsNICSMulticast Fedora23 is at libvirt 1.2.18, but you can get newer packages (of libvirt and other virt packages e.g. qemu) by enabling the virt-preview repo: https://fedoraproject.org/wiki/Virtualization_Preview_Repository (Note that you can also connect qemu:///session guests to a bridge via the qemu-bridge-helper. Just add the proper line to /etc/qemu/bridge.conf, and configure the interfaces with <interface type='bridge'> ... This will allow them to not only communicate with each other, but also with the rest of the external network, if the bridge is properly connected to the outside).
Awesome! Thanks for this update.